READING
Read the following passage about vacuums. Then answer questions 9-14 in your
answer booklet.
Pressure: Vacuums Are All About Nothing
by Bill Nye & Ian Saunders
Air pressure acts in all directions. But what
if there's no air at all?
Please consider the following:
When there's a place or a space with no air,
we call it a vacuum. Vacuum comes from an
old word that means "empty." Usually, things
that we call empty aren't really empty. They're
filled with air. An empty room may not have
any books or chairs or goldfish in it, but it's got
wall-to-wall air! And you know that air is made
up of molecules and that these molecules go
around bumping into things, making pressure.
A vacuum, though, is really empty. I mean
empty of everything—including air molecules.
And when there are no air molecules, we get
no air pressure.
A good example of a vacuum is a suction
cup stuck to a wall. When you push down on
the suction cup to attach it to the wall, you
force almost all of the air out from under it.
That creates a vacuum between the suction cup
and the wall. At the same time, the air pressure
in the room pushes against the other side of the
suction cup. The vacuum under the suction cup
has no air molecules and no air pressure, so
it doesn't push back. The air molecules in the
room hold the cup tightly to the wall.
The vacuum under a suction cup doesn't
last very long. Air molecules in the room are
constantly pushing against all sides of the
suction cup. Since there's a vacuum under the
suction cup, there's nothing to push back and
keep air molecules from getting through tiny
gaps between the wall and the cup. That means
that some of the air molecules from the room
can slowly sneak through into the space under
the suction cup. Eventually enough molecules
will sneak in, and the suction cup will fall off.
That's why we sometimes wet a suction cup
to make it stick better. The liquid fills in tiny
gaps between the cup and the wall. They're
small to us, but they're plenty big enough for
air molecules to slide through. See, it's harder
for air to get through the gaps when they're
filled with water, so the vacuum lasts longer.
Soda straws are another way to see a
vacuum in action. When you suck up a
milkshake, you suck most of the air molecules
from the straw into your mouth, making a
vacuum in the straw. Then the air pressure
in the room pushes down on the top of the
milkshake and pushes it up through your
straw. Right into your mouth. Mmmm!
Grade 7 Reading Item Sampler 2006-2007
17
READING
Of course, when people talk about a
vacuum, they usually mean a machine that
cleans the floor. But that kind of vacuum works
because it has a vacuum inside of it.
See, the motor inside the vacuum cleaner
blows almost all of the air out of the machine,
making a partial vacuum inside the machine.
Then, air in the room rushes in to fill the empty
space the only way it can—through the end of
the long hose you move over the carpet. All
that air rushing in carries dirt up off the floor.
Va-va-va-voom!
A.2.4.1
10. According to the passage, tiny gaps
between a suction cup and a wall will
A
B
C
D
keep the cup stuck tightly to the wall.
allow air molecules to get under
the cup.
force air molecules to push down
on the cup.
help create a vacuum between the cup
and the wall.
A.2.4.1
9.
Which statement best summarizes the
main idea of this passage?
A
A.2.3.1
11. In the passage, soda straws are used as
an example of how vacuums are
A
B
C
D
difficult to make.
created by liquids.
useful in everyday life.
ruined by air molecules.
B
C
D
"All that air rushing in carries dirt
up off the floor."
"The vacuum under a suction cup
doesn't last very long."
"And when there are no air
molecules, we get no air pressure."
"Eventually enough molecules will
sneak in, and the suction cup will
fall off."
Grade 7 Reading Item Sampler 2006-2007
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READING
A.2.4.1
12. According to the passage, what is a
vacuum?
A
B
C
D
a space that has no air
a liquid pressing on air
a gap that allows air to pass
a collection of air molecules
A.2.4.1
14. Which would be the best new title for
this passage?
A
B
C
D
"How Vacuums Work"
"Why Vacuums Are Important"
"How to Use a Vacuum Cleaner"
"The History of the Vacuum
Cleaner"
B.3.3.1
13. Information in this passage is presented
through
A
B
C
D
expert opinions.
specific examples.
problems and solutions.
comparing and contrasting.
Grade 7 Reading Item Sampler 2006-2007
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